1. Field of the Invention
The present invention relates to a final reduction gear unit for transmitting a driving force transmitted from a drive shaft (for example, a transmission output shaft) of an automobile or the like to axles extending transversely of a vehicle body so as to link up with left and right wheels, and more particularly to a lubricating construction for the final reduction gear unit.
2. Description of the Related Art
Generally speaking, a final gear reduction unit is a device provided for reducing the speed of a rotational driving force from a drive shaft of an automobile or the like for transmission to left and right axles linking up with left and right wheels. The final gear reduction unit is constituted by a small diameter pinion gear which rotates when receiving a rotational driving force from the drive shaft and a large diameter ring gear meshing with the small diameter pinion gear and linking up with the axles coaxially which are both disposed within a housing. Note that normally there is provided a differential mechanism between the large diameter ring gear and the left and right axles, whereby the rotational driving force from the large diameter ring gear is split so as to be transmitted to the left and right axles by the action of the differential mechanism. In the final reduction gear unit constructed as described above, lubricating oil is supplied into the housing, and the lubricating oil so supplied in the housing is then thrown up in response to the rotations of respective gears or the like for lubrication of respective portions, and it is common practice that a forced lubrication using an oil pump is not performed. In this case, there occurs a demand for sufficiently supplying the lubricating oil thrown up by the rotations of the gears or the like to portions within the housing which need lubrication.
From this reason, JP-B-2-62412 discloses the lubrication of a side bearing by providing an oil gutter for collecting lubricating oil thrown up by the rotations of a large diameter drive gear and a gear box (a gear box accommodating therein a differential mechanism), and guiding the thrown up lubricating oil to a side bearing through the oil gutter for lubricating the side bearing. A final reduction gear unit disclosed in this publication is a so-called a final reduction gear unit provided in a transverse-mounted transmission, and spur gears (spur wheels) are used for a small diameter drive gear and the large diameter drive gear. According to the construction of the final reduction gear unit disclosed, only the lubrication of the side bearing is required which rotatably supports the large diameter drive gear and the gear box integrally assembled to the large diameter drive gear and having the differential mechanism. Note that the small diameter drive gear is disposed on an output shaft of the drive shaft, and the sufficient lubrication is performed within the housing.
Additionally, JP-A-3-118350U discloses a final reduction gear unit comprising a small diameter pinion gear adapted to be rotatively driven when output rotations of a transmission are transmitted thereto via a propeller shaft and a large diameter ring gear meshing with the small diameter pinion gear and linking up with left and right axles coaxially via a differential mechanism, which are both accommodated and disposed within a housing. This publication also discloses a construction in which a bearing for rotatably supporting the small diameter pinion gear is lubricated. Note that the large diameter ring gear is rotatably supported by a bearing relative to the housing such that the ring gear freely rotates about a shaft extending in a transverse direction of a vehicle (a lateral direction), while the small diameter pinion gear is rotatably supported by the separate bearing relative to the housing such that the pinion gear freely rotates about a shaft extending a longitudinal direction of the vehicle.
In the final reduction gear unit, however, in which the small diameter pinion gear and the large diameter ring gear are disposed within the housing as described above, since the respective portions are in general constructed to be lubricated with the lubricating oil thrown up by the rotation of the gear (namely, since there is adopted no construction in which an oil pump is used for forced lubrication), it is very significant how the thrown up lubricating oil is distributed and supplied properly to those portions needing lubrication. Even in the related art constructions described above, there have been devised various ideas on how to supply the lubricating oil, but it is now desired that the supply of lubricating oil is performed with a further appropriate distribution of lubricating oil.
The present invention was made in view of these situations, and an object thereof is to provide a lubricating construction for a final reduction gear unit in which a small diameter pinion gear and a large diameter ring gear are disposed within a housing, wherein a bearing for rotatably supporting the small diameter pinion gear and a bearing for rotatably supporting the large diameter ring gear are supplied with lubricating oil under a proper distribution and in a sufficient amount at all times.
With a view to attaining the above object, according to an aspect of the invention, there is provided a final reduction gear unit constructed so as to have a small diameter pinion gear adapted to be driven to rotate by receiving output rotations from a drive shaft, a large diameter ring gear meshing with the small diameter pinion gear and linking up with left and right axles coaxially, a housing accommodating therein the small diameter pinion gear and the large diameter ring gear, first bearings (for example, taper roller bearing 26a, 26b in an embodiment) for rotatably supporting the large diameter ring gear relative to the housing, and second bearings (for example, taper roller bearings 15a, 15b in the embodiment) for rotatably supporting the small diameter pinion gear relative to the housing. Then, a gutter member is provided for receiving a part of lubricating oil which is thrown up by the rotation of the large diameter ring gear so as to be supplied to the second bearing in a splashing fashion, and a lubricating oil supply path (for example, first and second lubricating oil supply holes 6a, 6b, 7a, 7b in the embodiment) is formed in the housing (for example, comprising a housing 1 and retainers 5a, 5b in the embodiment) which links up with the first bearings at one end and with the gutter at the other end thereof.
In the lubricating construction constructed as described above, in transmitting output rotations of the drive shaft to the left and right axles and wheels via the final reduction gear unit, when the lubricating oil within the housing is thrown up by the rotation of the large diameter ring gear, the lubricating oil so thrown up is then supplied to the second bearing in a splashing fashion. However, the part of the lubricating oil is received in the gutter member and is supplied into the lubricating oil supply path for supply to the first bearings via the lubricating oil path, and therefore, not only the second bearings but also the first bearings are properly lubricated at all times.
Preferably, a splash guide space is formed in the housing for guiding the lubricating oil thrown up by the rotation of the large diameter ring gear toward the second bearing in a splashing fashion, and the gutter member is provided such that the gutter member extends in a transverse direction so as to partially close the splash guide space. According to this construction, the lubricating oil thrown up by the rotation of the large diameter ring gear is then splashed on the second bearing through the splash guide space for lubricating the second bearing, and simultaneously, a part of the lubricating thrown up is received in the gutter member for supply to the first bearings, whereby the first bearings are lubricated. Namely, both the first and second bearings are properly lubricated at all times.